This disclosure relates to electrochemical cells, and, more particularly, to an apparatus and methods for sensing and controlling the liquid level in an electrolysis cell utilizing the protonic rate.
Electrochemical cells are energy conversion devices, usually classified as either electrolysis cells or fuel cells. Proton exchange membrane electrolysis cells can function as electrolysis cells by electrolytically decomposing water to produce hydrogen and oxygen gases. Referring to FIG. 1, a section of an anode feed electrolysis cell of the prior art is shown generally at 10 and is hereinafter referred to as xe2x80x9ccell 10.xe2x80x9d Reactant water 12 is fed into cell 10 at an oxygen electrode (anode) 14 to form oxygen gas 16, electrons, and hydrogen ions (protons) 15. The chemical reaction is facilitated by the positive terminal of a power source 18 connected to anode 14 and the negative terminal of power source 18 connected to a hydrogen electrode (cathode) 20. Oxygen gas 16 and a first portion 22 of the water are discharged from cell 10, while protons 15 and a second portion 24 of the water migrate across a proton exchange membrane 26 to cathode 20. At cathode 20, hydrogen gas 28 is removed, generally through a gas delivery line. The removed hydrogen gas 28 is usable in a myriad of different applications. Second portion 24 of water is also removed from cathode 20.
Second portion 24 of water, which is rich in hydrogen, is recovered by a hydrogen/water phase separation apparatus (described below). The hydrogen/water phase separation apparatus allows the hydrogen entrained in second portion 24 of water to diffuse from the water and into the vapor phase above second portion 24 of water. The hydrogen is then recovered, and water is returned to the system to supplement reactant water 12. The hydrogen/water phase separation apparatus is of a limited volumetric capacity; therefore, second portion 24 of water accommodated therein oftentimes must be returned to the system before all of the entrained hydrogen gas can diffuse out of second portion 24 of water. In such a system, the level of water in the hydrogen/water phase separation apparatus has heretofore been sensed and controlled using conventional level sensing and controlling techniques.
The detection and control of the water level in the hydrogen/water phase separation apparatus involves the disposition of sensing equipment directly into either or both the liquid and the vapor phase above the liquid. One of the most common methods of detecting and controlling the liquid level in the hydrogen/water phase separation apparatus (or any other type of containment vessel) involves measuring the difference in static pressure between two fixed elevations, one of the fixed elevations being in the vapor phase above the liquid and the other fixed elevation being below the liquid surface. The differential pressure between the two fixed elevations is directly related to the liquid level in the hydrogen/water phase separation apparatus. One of the problems associated with such a method derives from the buildup of condensation in the line from which the static pressure in the vapor phase is measured. If the line fills up with condensate, the differential pressure will be zero even if the liquid level is near the fixed elevation in the vapor phase. Such a false reading may be interpreted by an operator as indicative of the vessel being empty. Other methods of detecting and controlling liquid and vapor levels pose similar problems.
When equipment required for the sensing and control of liquid levels is installed such that the liquid levels are at least partially dependent upon the pressure of the system into which they are incorporated, cautionary measures must generally be incorporated into the process to ensure that all of the equipment remains fully functional. Such cautionary measures oftentimes require ongoing maintenance in order to allow for the maximum operability of the equipment with as little downtime as possible. Ongoing maintenance, however, generally adversely affects the overall cost of the process.
While existing electrolysis cell systems are suitable for their intended purposes, there still remains a need for improvements, particularly regarding the management of the separation of the hydrogen gas from the water. Furthermore, a need exists for improved sensing and control of the level of the water in the hydrogen/water phase separation apparatus during the operation of the associated electrolysis cell system.
A level sensing system for determining the level of a liquid in a hydrogen/water phase separation apparatus associated with an electrolysis cell comprises a flow control device disposed in fluid communication with a liquid outlet stream of the hydrogen/water phase separation apparatus and a controller disposed in operable communication with the flow control device. The controller is configured to receive and quantify input data corresponding to a measure of the rate of generation of hydrogen gas from the proton exchange membrane electrolysis cell.
A method of maintaining a level of a liquid in a hydrogen/water phase separation apparatus disposed in fluid communication with a proton exchange membrane electrolysis cell comprises deriving a rate of generation of hydrogen gas in a cell stack of the electrolysis cell, transmitting the rate of generation of the hydrogen gas to a flow control device, and adjusting the flow rate of the liquid exiting the hydrogen/water phase separation apparatus correspondingly with the rate of generation of hydrogen gas in the cell stack.